Modelling of reinforced concrete structures in fire

Abstract

In this paper a robust finite-element procedure is presented for three-dimensional modelling of reinforced concrete structures under fire conditions. In this non-linear procedure a reinforced concrete building is modelled as an assembly of finite plain beam–column and slab elements, reinforcing steel bar elements and bond-link elements. Both material and geometric non-linearities are considered in the model. To consider the effects of concrete spalling on the thermal and structural behaviours of concrete structures under fire conditions, a ‘void layer' and ‘void segment' are introduced to represent the spalled-concrete part within concrete slabs, beams and columns. A critical temperature is used as the concrete spalling criterion. These developments enable the model to simulate quantitatively the effects of concrete spalling on both the thermal and structural behaviours of reinforced concrete structures in fire. A series of analyses are also conducted on a generic reinforced concrete building. The results indicate that, under fire conditions, the structural behaviour of isolated members with the concrete spalled is very different compared with the behaviour exhibited when embedded within a building. The influence of bond conditions between concrete and reinforcing steel bars on the fire resistance of structural members is significant. The global structural fire resistance of the reinforced concrete building is significantly affected by the concrete spalling on their members, in which the most important member is floor slabs.